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Exploiting reciprocal space: Electron diffraction, textures and precession
Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
Responsible organisation
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Electron crystallography emerges as a new tool for accurate structure determination of very small crystals. In order to exploit the full potential of electron diffraction, the methods for data acquisition and processing have to be developed towards the high standards of X-ray crystallography. Spot diffraction patterns give complete separation of reflections and provide two-dimensional data sets. Separation of reflections occurs also in texture patterns; the whole or almost whole reciprocal lattice is represented on them in two dimensions. In order to speed up texture pattern analysis and improve the accuracy, the program TexPat was developed for quantification of texture patterns. It introduces new approaches for automated detection of centre and symmetry axes and simplifies the process of indexing and estimating the intensities of all reflections.

The precession technique, developed by Vincent and Midgley at the University of Bristol in 1994, has become available to the TEM users because of recent hardware implementations that allow data acquisition of sufficient quality for structure determination. Dynamical interactions can be effectively reduced using the precession method, and the intensity data can be treated within the kinematical approximation. However, a deeper understanding of the theory is necessary. A program eMap has been developed which performs kinematical and dynamical simulations of precession electron diffraction patterns. A set of algorithms was introduced for indexing of precession patterns with HOLZ present, estimation of three-dimensional lattice parameters and crystal symmetry deduction using both ZOLZ and HOLZ. All developed algorithms were implemented in the diffraction simulation program eMap and electron diffraction analysis program ELD. Both oblique texture and precession electron diffraction patterns provide intensities of high quality, which can be treated kinematically for further crystal structure solution.

However, there is also the fundamental phase problem in crystallography. For quasicrystal approximants, the strong reflections approach allows overcoming this problem and deducing structural models from already known structures. In order to perform the analysis of quasicrystal approximant structures in real and reciprocal space, the eMap program was used. The operations included in the program allow the calculation of three-dimensional electron density or potential maps; peak search, calculation of theoretical structure factors both for X-rays and electrons (kinematical and dynamical); visualization of reciprocal space and phase values of reflections in specified colouring scheme.

Place, publisher, year, edition, pages
Stockholm: Institutionen för fysikalisk kemi, oorganisk kemi och strukturkemi , 2006. , 96 p.
Keyword [en]
electron crystallography, electron diffraction, texture patterns, precession electron diffraction
National Category
Inorganic Chemistry
Identifiers
URN: urn:nbn:se:su:diva-791ISBN: 91-7155-188-3 (print)OAI: oai:DiVA.org:su-791DiVA: diva2:199280
Public defence
2006-01-27, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 12 A, Stockholm, 10:00
Opponent
Supervisors
Available from: 2006-01-05 Created: 2006-01-05Bibliographically approved
List of papers
1. TexPat – a program for quantitative analysis of oblique texture electron diffraction patterns
Open this publication in new window or tab >>TexPat – a program for quantitative analysis of oblique texture electron diffraction patterns
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2004 In: Zeitschrift für Kristallographie, Vol. 219, 12-19 p.Article in journal (Refereed) Published
Identifiers
urn:nbn:se:su:diva-25267 (URN)
Note
Part of urn:nbn:se:su:diva-791Available from: 2006-01-05 Created: 2006-01-05Bibliographically approved
2. A Practical Method to Detect and Correct for Lens Distortion in TEM
Open this publication in new window or tab >>A Practical Method to Detect and Correct for Lens Distortion in TEM
2006 In: Ultramicroscopy, Vol. 106, no 2, 66-74 p.Article in journal (Refereed) Published
Identifiers
urn:nbn:se:su:diva-25268 (URN)
Note
Part of urn:nbn:se:su:diva-791Available from: 2006-01-05 Created: 2006-01-05Bibliographically approved
3. Quantification of texture patterns
Open this publication in new window or tab >>Quantification of texture patterns
2006 In: Electron Crystallography.: Novel Approaches for Structure Determination of Nanosized Materials., 2006, 121-142 p.Chapter in book (Other academic) Published
Identifiers
urn:nbn:se:su:diva-25269 (URN)
Note
Part of urn:nbn:se:su:diva-791Available from: 2006-01-05 Created: 2006-01-05Bibliographically approved
4. A structure model for τ(μ) phase in Al-Cr-Si alloys deduced from λ phase by the strong reflections approach
Open this publication in new window or tab >>A structure model for τ(μ) phase in Al-Cr-Si alloys deduced from λ phase by the strong reflections approach
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2006 (English)In: Acta Crystallographica Section B: Structural Science, ISSN 0108-7681, E-ISSN 1600-5740, Vol. 62, no 1, 16-25 p.Article in journal (Refereed) Published
Abstract [en]

There are very obvious common features in the electron diffraction patterns of the λ and τ(μ) phases in the Al–Cr–Si system. The positions of the strong reflections and their intensity distributions are similar for the two structures. The relation of the reciprocal lattices of the λ and τ(μ) phases is studied. By applying the strong-reflections approach, the structure factors of τ(μ) are deduced from the corresponding structure factors of the known λ phase. Rules for selecting reflections for the strong-reflections approach are described. Similar to that of λ, the structure of τ(μ) contains six layers stacked along the c axis in each unit cell. There are 752 atoms in each unit cell, 53 of them are unique. The corresponding composition of the τ(μ) model is Al3.82  −  xCrSix. Simulated electron diffraction patterns from the structure model are in good agreement with the experimental ones. The arrangement of interpenetrated icosahedral clusters in the τ(μ) phase is discussed.

Keyword
quasicrystal approximants • strong-reflections approach • electron crystallography.
National Category
Physical Sciences
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-25270 (URN)10.1107/S0108768105035779 (DOI)
Note
Part of urn:nbn:se:su:diva-791Available from: 2006-01-05 Created: 2006-01-05 Last updated: 2010-08-19Bibliographically approved
5. Structure relations in real and reciprocal space of hexagonal phases related to i-ZnMgRE quasicrystals
Open this publication in new window or tab >>Structure relations in real and reciprocal space of hexagonal phases related to i-ZnMgRE quasicrystals
2006 (English)In: Philosophical Magazine, ISSN 1478-6435, E-ISSN 1478-6443, Vol. 86, no 3-5, 343-348 p.Article in journal (Refereed) Published
Abstract [en]

The µ 3 , µ 5 and µ 7 approximants in Mg-Zn-RE were related in real and reciprocal space. The structure factors of µ 3 , µ 5 and µ 7 have quite similar intensity distributions and identical phases for the strongest corresponding reflections. Structure models of any of µ 3 , µ 5 and µ 7 can be obtained from any of the others using the strong reflections approach.

Place, publisher, year, edition, pages
Taylor and Francis Ltd, 2006
National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:su:diva-25271 (URN)10.1080/14786430500279658 (DOI)
Note
Part of urn:nbn:se:su:diva-791Available from: 2006-01-05 Created: 2006-01-05 Last updated: 2010-12-14Bibliographically approved
6. Structure of the pseudodecagonal Al–Co–Ni approximant PD4
Open this publication in new window or tab >>Structure of the pseudodecagonal Al–Co–Ni approximant PD4
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2006 (English)In: Philosophical Magazine, ISSN 1478-6435, E-ISSN 1478-6443, Vol. 86, no 3-5, 457-462 p.Article in journal (Refereed) Published
Abstract [en]

A model for the pseudodecagonal approximant PD4 in the Al–Co–Ni system was deduced from single crystal X-ray diffraction data. The space group is Bbmm with a ?=?101.3, b ?=?32.1 and c ?=?4.1?Å. Atomic positions of 133 unique atoms in the unit cell with a reasonable geometry were found by direct methods and the difference Fourier syntheses. The obtained structure model is in good agreement with high-resolution electron microscopy images of PD4. Diffuse scattering observed along the a * direction in the hkl layers with l ?=?1/2, 3/2 etc. indicates a superstructure with a doubling of the periodicity along the c -axis and a lamellar disorder along the a -axis. If this diffuse scattering is taken into account, c ?=?8.2?Å.

Place, publisher, year, edition, pages
Taylor and Francis, 2006
National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:su:diva-25272 (URN)10.1080/14786430500270343 (DOI)
Note
Part of urn:nbn:se:su:diva-791Available from: 2006-01-05 Created: 2006-01-05 Last updated: 2010-12-14Bibliographically approved
7. Extraction of intensities from oblique texture electron diffraction patterns by 2D pattern decomposition
Open this publication in new window or tab >>Extraction of intensities from oblique texture electron diffraction patterns by 2D pattern decomposition
Manuscript (Other academic)
Identifiers
urn:nbn:se:su:diva-25273 (URN)
Note
Part of urn:nbn:se:su:diva-791Available from: 2006-01-05 Created: 2006-01-05 Last updated: 2010-01-13Bibliographically approved

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